This application claims the priority of Application No. 101 60 478.5-51, filed Dec. 8, 2001, in Germany, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a system having a motor vehicle gearbox, which can facilitate reversal of the travel direction.
German Patent Document DE 198 30 953 A1 (corresponding U.S. Pat. No. 6,413,189) has already disclosed a system having a motor vehicle gearbox by means of which a reversal of the direction of travel of a motor vehicle can be initiated using a reversing mechanism. In addition, the system has a control unit for automatically reversing the direction of travel, it being possible for a person to select a reversal from forward travel to reverse travel or from reverse travel to forward travel by means of the control unit.
The control unit is constructed in such a way that after the selection of a reversal of the direction of travel by a person at a vehicle velocity above a specific limiting velocity, the vehicle velocity is automatically reduced by decreasing a transmission ratio of the infinitely variable motor vehicle gearbox under infinitely variable control.
In addition, the system has a vehicle brake unit which is separate from the motor vehicle gearbox and by means of which a person can increase the deceleration process of the motor vehicle.
U.S. Pat. No. 4,248,330 discloses a tractor for slow velocities at which the vehicle brakes are activated as soon as the driver of the vehicle switches over between forward travel and reverse travel. Here, the vehicle brake system and the gearbox is supplied with hydraulic fluid or pressure from one and the same pressure medium pump. When the gear speed is changed, the pressure in the brake system drops owing to the pressure spaces of the gearbox clutches being filled with hydraulic fluid. The vehicle brake of the tractor is spring-loaded so that the drop in pressure in the gearbox owing to the above-mentioned change of gear speed causes the tractor to be braked.
German DE 25 14 306 A1 (corresponding U.S. Pat. No. 3,910,389) discloses a load-lifting vehicle or tractor shovel which is braked during a gearbox shifting operation between the directions of the vehicle. The flow means of a pressure medium pump is directed here to a brake system and an anti-direction-reversal valve.
German DE 30 38 400 A1 (corresponding U.S. Pat. No. 4,386,688) discloses an automatic deceleration device for use by tracklaying vehicles in which an automatic deceleration takes place without the brake pedal and the deceleration pedal being depressed. If a vehicle velocity is predefined and the actual velocity is higher, automatic deceleration takes place and the gearbox is then shifted into a suitable position.
An object of the invention is to provide a system with a particularly wide area of application which additionally permits the drive train to be loaded as little as possible. This object is achieved according to certain preferred embodiments of the invention by providing a system for a motor vehicle having a motor vehicle gearbox by means of which a reversal of the direction of travel can be initiated, having a vehicle brake unit which is separate from the motor vehicle gearbox, and having a control unit wherein, when there is a reversal of the direction of travel from at least a first direction into a second direction when there is still a positive vehicle velocity (v) in the first direction, the control unit generates a braking torque (M) which reduces the vehicle velocity (v) by means of an actuator unit and by means of the vehicle brake unit, the direction of travel being sensed by means of a sensor unit.
The invention is based on a system for a motor vehicle having a motor vehicle gearbox by means of which a reversal of the direction of travel can be initiated, having a vehicle brake unit which is separate from the motor vehicle gearbox, and having a control unit.
It is proposed that, when there is a reversal of the direction of travel from at least a first direction into a second direction when there is still a positive vehicle velocity in the first direction, the control unit generates a braking torque which reduces the vehicle velocity, by means of an actuating unit and by means of the vehicle brake unit. The actual direction of travel is sensed here by means of a sensor unit which can be configured in particular as a rotational speed sensor on a wheel of the motor vehicle and by means of which the direction of rotation of the wheel can also be sensed. Consequently, the motor vehicle has to be braked only if it does not in any case already roll in the direction of travel selected as the objectivexe2x80x94i.e. the second directionxe2x80x94when the neutral setting N is inevitably passed. Likewise, if the vehicle already rolls in the direction of travel which is desired as the objective of the reversal of the direction of travel, the program sequence for braking the wheels can be modified. Consequently, depending on which direction of travel is sensed by the sensor unit, procedures for braking the vehicle which are different from the main program are processed in a controller of the vehicle brake unit. These different procedures can in particular result in different braking torques over the velocity. The system can basically be used in all motor vehicles with infinitely variable or incremental, partially automatic or fully automatic motor vehicle gearboxes, and in particular unnecessarily high loading of the motor vehicle gearbox and of the entire drive train can be avoided, specifically by using a brake unit which is separate from the vehicle gearbox. In addition, with the solution according to the invention, a braking torque of virtually any desired magnitude can be generated independently of a selected setting of the motor vehicle gearbox, specifically in particular even in a neutral setting of the motor vehicle gearbox.
The actuator unit which is assigned to the vehicle brake unit can be formed by an actuator which is already present, for example by an actuator of an electronic stabilization program (ESP) and/or particularly advantageously by an actuator for generating a complete braking pressure, which is actuated electrically by means of a pedal in the motor vehicle, as a result of which additional actuating means can be avoided. However, it is also contemplated for one or more actuators to be additionally provided for the system.
As a result of the refinement of a vehicle brake unit which is separate from the motor vehicle gearbox, it is possible, in a particularly advantageous way, to use different actuator systems for the motor vehicle gearbox and the separate vehicle brake unit, that is to say both the gearbox and the vehicle brake unit can be actuated hydraulically, electrically or pneumatically. Here, the actuator systems can differ from one another so that, for example, the gearbox is actuated electrically, whereas the vehicle brake unit is an electrohydraulic system. In the case of gear-shifting operations from the forward travel gear speed D to the reverse travel gear speed R and vice versa when using a hydraulic gearbox, the separation advantageously results in the brake pressure not being directly dependent on the pressure drop owing to the filling of the pressure spaces of the gearbox clutches with hydraulic fluid. This separation also entails efficiency advantages as it is necessary to maintain a brake system pressure of 150 bar for an electrohydraulic brake system whereas a customary automatic gearbox requires only a working pressure of 25 bar.
If the control unit initiates at least one switching-over process in the motor vehicle gearbox only starting from a defined vehicle velocity, it is also possible to avoid unnecessary high loading, and in addition savings in terms of locking mechanisms can be achieved, or at least the function of locking mechanisms can be supported.
In a further refinement of the invention, it is proposed that the control unit be formed at least partially by a controller for the motor vehicle gearbox and by a controller for the vehicle brake unit. Existing components can be advantageously used and there can be a reduction in terms of additional components, installation space, weight, expenditure on assembly and costs.
If the control unit sets, as a function of at least one operating parameter, the magnitude of the braking torque generated by means of the actuator unit and the vehicle brake unit, for example along one or more functions in accordance with one of more characteristic diagrams, a braking process which is particularly advantageously adapted to the peripheral conditions and a reversal of the direction of travel which is advantageously adapted to the peripheral conditions can be achieved. The process can be made dependent on various operating parameters which appear appropriate to a person skilled in the art, for example as a function of a currently sensed or permanently stored motor vehicle weight, as a function of prevailing carriageway conditions, positive gradient of the carriageway and in particular as a function of a sensed vehicle velocity.
The necessary information can be sensed by means of specially provided sensors or advantageously read out of a data network of the motor vehicle, for example by means of a CAN (Controller Area Network) bus, as a result of which already existing sensors can at least largely be used.
In addition, a jolting movement of the motor vehicle can advantageously be avoided or a uniform movement obtained, thus increasing comfort, if, at the start of a reversal of the direction of travel, the control unit generates a braking torque which rises along a function, and/or at the end of a reversal of the direction of travel generates a braking torque which decreases along a function.
Further advantages emerge from the following description of the drawing. The drawing illustrate an exemplary embodiment of the invention. The description and the claims contain numerous features in combination. A person skilled in the art will advantageously also consider the features individually and combine them to form further appropriate combinations.